Calculate Relative Atomic Mass (Edexcel IGCSE Chemistry: Double Science)
Revision Note
Author
StewartExpertise
Chemistry Lead
Calculate Relative Atomic Mass
How to Calculate Relative Atomic Mass
- The relative atomic mass of each element is calculated using the mass number and the relative abundances of all the isotopes of a particular element
- To calculate the relative atomic mass:
- Multiply the % abundance of each isotope by its mass
- Add these numbers together
- Divide by the total abundance (which when using % abundance, will be 100%)
- Here it is as an equation:
- The top line of the equation can be extended to include the number of different isotopes of a particular element present
- So, if there were 3 isotopes present then the equation would read:
Worked example
The table shows information about the Isotopes in a sample of rubidium with 72% 85Rb and 28% 87Rb
Use information from the table to calculate the relative atomic mass of this sample of Rubidium. Give your answer to one decimal place.
Answer:
Relative Atomic Mass = 85.6
Exam Tip
Isotopes are easy to recognize from their notation as they have the same symbol but different mass numbers. For example, the two stable isotopes of copper are 63Cu and 65Cu
You've read 0 of your 0 free revision notes
Get unlimited access
to absolutely everything:
- Downloadable PDFs
- Unlimited Revision Notes
- Topic Questions
- Past Papers
- Model Answers
- Videos (Maths and Science)
Did this page help you?